1. Field of the Invention
The present invention relates to light fixtures generally and, more particularly, but not by way of limitation, to a novel light fixture that is especially useful as a rear end marker for trains operating in the United States.
2. Background Art
While the present invention is described with reference to providing a rear end marking device for trains, the present invention is useful in a variety of applications.
In November 1977, the Federal Railway Administration (FRA) in response to a Law passed by Congress provided a Final Report covering guidelines for testing rear end marking devices for all trains operating in the United States. The Law was in reaction to a serious rear end collision where many passengers were injured and some were killed. The guidelines require a minimum of 100 candela straight on and 50 candela at plus and minus 15 degrees in the horizontal plane. The guidelines also required 50 candela at plus and minus 5 degrees straight on in the vertical plane. The maximum light level allowed is 1,000 candela. All light intensities were measured at the light source.
All fixtures at that time were lighted by incandescent lamps. Many of these lamps had a lamp life of 800 hours which presented a maintenance cost to the railroads because of frequent lamp replacements. The incandescent lamps also presented a safety problem, since, upon failure of an incandescent lamp, the lamp immediately becomes unlighted. With the development of LEDs having a long life, estimated in the 50,000 hour range, interest developed in creating LED rear end marker lights for trains. New lights were developed with many LEDs, perhaps as many as 50-70 LEDs facing away from the reflectors, and are now very common in traffic lights. An advantage of LEDs over conventional incandescent lamps, in addition to having a much longer life, is that, when LEDs age, they typically become darker and do not immediately become unlighted.
Accordingly, it is a principal object of the present invention to provide a light fixture that uses only a few LEDs.
A further object of the present invention is to provide such a light fixture that achieves the required oval pattern without wasting light energy in the vertical area above and below the horizontal pattern required by the FRA guidelines.
An additional object of the invention is to provide such a light fixture that achieve the required light beam with light energy distributed in a cone required by the guidelines in a very efficient manner.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.